Electric motor



B AQSPBRM ELECTRIC MOTOR,

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UNITED STATES PATENT OFFICE.

ELMEE A. srEnRY, or oHioAco, ILLiNois.

ELECTRIC MOTOR.

SPECIFICATION forming part of Letters Pat/ent No. 353,987, dated December 7, 1886.

Application filed October 13, 1883. Serial No. 108,912. (No model.)

To all whom it may concern:

Be it known that I, ELMER A. SPERRY, a citizen of the United States, residing at Chicago, in the county of Cook and State of Illinois, have invented certain new and useful Improvements in Electric Motors, of which the following is a specification, reference being had therein tothe accompanying drawings.

This invention relates to an improvement in electric motors of that class in which the field-magnets are excited by au electric cnrreut on a derivation from the main circuit which supplies the motive current to the armature.

It is well known that when the armature of an electric motor isrotated at high speed a counter electro-motive force is developed therein', which very seriously connteracts the main current, and frequently so reduces the capacityo'fthe machine as to render it ineffective for many purposes. Electric motors have been constructed with resistances so proportioned that the maximum development of power is at high speeds; but in such machines is found the disadvantage that at low speeds their power is disproportionately small, so

that a comparatively7 high speed must be maintained, even when butlittle power is requiredv to be exerted by the machine. I

It is the object of my improvement to cause the counter electro-inotive force developed in the armature to so act upon the field-magnets as to augment the magnetism thereof in almost the exact ratio that the energy in the armaturc is depreciated by the counter-current, thus rendering the resultant 'from the joint forces of armature and eld a practically uniform quantity, not affected appreciably by the .which represents adiagrammatic front viewof an electric motor provided with my improvements. f

The letter A indicates the rotary armature,

and B B the pole-pieces of the field-magnets of said helices not being shown as the manner of their connection in the derived circuit will be readily understood. In this derived circuit is alsoinclnded an adjustable rheostat, K, so that the current which excites the field-magnets can be regulated as desired.

L and M are the wires of a sub-shunt or derivation, which will be hereinafter referred to.

The operation of the devices for preventing f` adverse effect of the counter electro-motive force developed in the armature will be uu-I derstood from the following explanation: The resistance of the iield is such that by slight eXtra adj nstment of the rheostat K it is accurately proportioned to that of the armature. 'When the motor starts and runs at low speed, the opposing electro motive l'orce developed in the armature is slight, and the energy in each derivation ofthe circuit is practically in proportion to the resistance of the conductors, the resistance of the iield-coils being such that the magnetism developed inthe pole-pieces B Bis below the point of magnetic saturation of the iron. Now, when the speed of the armature increases, the counter current developed in its coils tends in opposite direction to the current traveling ou the main conductors H and G to the points ol junction of wires J i main current backward tothe junctions oi' roo wires J and I with the main conductors G and I-I, where passage is oiered of uniform resist-`y ance, so that an increase of current Hows in a derivation including the :field-coils and augments the magnetism of the field-magnets as the energy of the armature is decreased, thus` making the resulting force of the united energies of the armatures and ield a practically constant quantity, as before stated.

It sometimes happens that there is developed in the field-magnets a tendency to reach their saturate points too early-that is, before the speed of the armature has sufficiently increased after being started. In order to preventthis I have provided the following devices.

The letter It indicates a variable rheostat, one end of which is connected through the coil of an axial magnet, S, with the wire J of the field-circuit, an'd the pivoted shunting-arm R of this rheost'at is connected by wire M with the wire I ofthe iield-circuit, so that the rhe'ostat R and magnet S are in a sub-shunt or derivation from the field-circuit. The arm R is held toward the end of the rheostat, to which the wire L is attached by means of spring r, said arm resting against an adjustable stop, r, by which its normal position with respect to the coils of the rhcostat may be determined. To the opposite side of the arm, It is attached one end ot' a cord, T, the other end of which is secured to a shaft, T, upon which is xed a toothed wheel, Ti. Directly under this wheel is pivoted an arm, T3, to the upper end of which is pivoted one end of a pawl, t, the other end of which is arranged to be engaged at the proper time with the teeth of wheel T2, as will presently appear. A pawl, t', is arranged to prevent said wheel from turning under the influence ofspring r, The pawl t' is connected by a cord, t, with the free end of a lever, S', which is pivoted above the wheel T2 by aiixed pivot near the end to which the cord t is attached, the other end of the lever being pivoted to the lower end of the movable core S2 ofthe magnet S, the downward movement or" which is limited by a suitable stop, s. To one side ofthe arm 'I3 is connected one end of an arm, T1, the other end of which is pivoted to a vibratory arm, T5, which is connected by a pitmanrod, T, with a wrist-pin projecting iront a toothed wheel, T7, which gears with a toothed wheel,y TS, iixed upon a shaft, T, which carries a belt-pulley, T10, this beltpul ley being connected with a similar pulley, c, on the shaft ofthe armature by means of a belt, F.

It will now be observed that when the armatuieshaft is in rotatioma rotary motion will be communicated to wheel TS and thence to the wheel T7, from which a vibratory motion will bc transmitted through the rod Is to arm T5, and from this arm a similar Amotion will be communicated to the arm T through rod T4, so that while the motor is in operation the arm T will be kept in constant vibration. When the magnet S is not excited, its core SZ will rest upon the stop s, and the end of lever S will be held in such position that the pawl t, supported from the lever S by the cord t3,

will be out of engagement with the wheel T2; i

but when said magnet is excited the pawlt Vdraw the arm It in the direction indicated by the arrow on the rheostat, so as to include adf ditional resistance in the circuit in which said rheostat is connected.

The operation of these devices is as follows: 1When, owing to the strength of the main cur- :rent and the derivation thereof in the eldcircuit, there is a tendency of the field-mag nets to reach their saturation-point before the armature has attained a sullicient speed,a portion of the current in the iield-circuit will be diverted through the subderivation, indicated by the letters L and M, and thus the current in the field-circuit will be reduced suiiiciently to prevent the magnetic saturation of the iron in the tieldmagnct cores. The quantity of current in the field-circuit will, however, be gradually increased,owiug to the fact that the current in the subderivation excites the magnet S and causes its core to be drawn upward, thus raising the pawl t into engagement with the wheel Ti, so that said wheel will be turned, causing the cord T to be wound up slowly and gradually move the arm It to such position that a suiiicient resistance ot' the rheostat R will be included in the suhderivation to drive the current back to the held-circuit, or, rather, to prevent its being diverted therefrom. When this condition of atliairs is reached, the magnet S ceases to be excited, and the pawl t is lowered ontofengagement with the wheel T2, which is, however, prevented from turning backward by the pawl t, this pawl being IOO thrown out of engagement to allow the rheostat It to resume its normal condition when the motor is stopped.

It will now be seen that by the devices I have described andjust explained the current in the field-circuit is preventedfrom being too strong at the start, however strong may be the main current supplied to the armature, and will be gradually increased in sti engtli,so that the cores ofthe held-magnets will not reach the point of saturation until the armature has had ample time tol attain a proper speed of rotation.

Thebrush esD D and D D are arranged for alternate contact with the commutator by means of mechanism connected with a friction-clamp, T, which embraces the shaft T. readily observed that this friction-clamp and devices connecting the same with the brushes will serve to change the direction of rotation of the shaft T1g whenever there is a change of direction in the armature.

Having now fully described my invention, and explained the operation thereof, I claiml. In an electric motor, the combination,

with a circuit derived from the main circuit and arranged to excite the field-magnets, ofa subderivation from said derived field-circuit and an automatic rheostat included in said IIO It will be solenoid-core, and mechanical devices, substantially as described, for moving the toothed wheel and adjusting the rheostat from the shaft of the motor, substantially as set forth.

In testimony whereof I aflix my signaturein presence of two Witnesses.

ELMER A. rSPERRY.

Witnesses:

LOREN GREENE, ALLEN A. GRIFFITH, 

